We are using some C++ UDF in vertica with FENCED option since it is safe. Can anybody tell what are the risks which we might face when using FENCED mode ?
As I see it , mostly performances ( according to Vertica doc around 10% degradation ) , but I believe that its very related to your use case .
You probably should see more CPU context switching as two process (instead of one ) are processing the request
I've seen fenced UDFs perform as much as 20x slower. As Eli said, it depends on the use case.